CNC Machined from solid Billet 7075 Aluminum. If you want to build a high end UltraMatch Upper, look no further than the Rainier Arms UltraMatch Billet Upper.

The most critical features are:

* Parallelism between the picatinny rail, main center bore and the centerline of the mounting lugs
* Perpendicularity between the centerline of the lugs and the barrel mating face (at the front of the threads)
* Flatness of the barrel mating face

We are holding .0003 or better on all of those measurements. Competitor uppers are between .001 and .003 on the perpendicularity and parallelism.
Configuration:

Got the new Rainier 7.5" Pistol upper. The receivers look and fit amazing. Very happy with the purchase.

One thing I did notice is my rear Troy BUIS did not want to lay flat in the down position. I had to pull it to the left as I folded it down or else it would catch on the rail. It goes down but it's rubbing on the left side. Checked it with another upper and it didn't have the issue. Might want to keep an eye on that measurement.

This is my second Rainier upper and I wouldn't hesitate to buy another one. Top notch.